Adaptive membrane structure with insertable protrusions

ABSTRACT

The present invention relates to a porous adaptive membrane structure that has movable membranes. The structure can be made to change its gas, liquid or particulate permeability in response to surrounding environmental conditions. The application of this invention is includes protective apparel that is comfortable to wear wherein the level of protection provided is based on conditions in the environment. Hence, the protective apparel is highly breathable and comfortable in a non-hazardous environment but impermeable or only semipermeable in a hazardous environment.

This application claims the benefit of U.S. Provisional Application No.60/567,357, filed Apr. 30, 2004, which is incorporated in its entiretyas a part hereof for all purposes.

FIELD OF THE INVENTION

The present invention relates to an adaptive membrane structure that hasmovable membranes. In one embodiment, the structure can be made tochange its liquid or vapor permeability in response to surroundingenvironmental conditions. The application of this invention includes anarticle such as protective apparel that is comfortable to wear whereinthe level of protection provided is based on conditions in theenvironment. Hence, the protective apparel is highly breathable andcomfortable in a non-hazardous environment but semipermeable orimpermeable in a hazardous environment.

TECHNICAL BACKGROUND OF THE INVENTION

There is a growing need for personal protective apparel that guardsagainst toxic chemical and biological agents. These agents may be

-   -   (a) accidentally released in a chemical manufacturing plant, in        a scientific or medical laboratory or in a hospital;    -   (b) released intentionally during wartime by a government to        attack the military forces of the opposition; or    -   (c) released during peacetime by criminal or terrorist        organizations with the purpose of creating mayhem, fear and        widespread destruction.

For this reason, the United States military and other defenseorganizations of countries all over the world have sought to provideadequate protection against chemical and biological warfare agents. Theneed for such protective apparel also extends to police departments,fire departments, emergency responders and health care providers. Theseorganizations are responsible for providing assistance and relief aftera catastrophic release of chemical or biological toxins, but they cannotdischarge their responsibilities without adequate protection (“ChemicalProtective Clothing for Law Enforcement Patrol Officers and EmergencyMedical Services when Responding to Terrorism with Chemical Weapons”,Arca, V. J. and Marshall, S. M., in report of the Chemical Weapons,Improved Response Program, U.S. Army Soldier and Biological ChemicalCommand, November 1999).

According to the Handbook of Chemical and Biological Warfare Agents (D.Hank Ellison, CRC Press, Boca Raton, Fla., 1st edition, 1999), mostchemical warfare toxins are fatal at concentrations as low as 1 part permillion (ppm). Hence, to provide adequate protection from chemicalwarfare agents, a protective suit has to be almost impermeable to suchchemicals. It is not difficult to devise structures that are impermeableto toxic chemical vapors and liquids, but such structures are also hot,heavy and uncomfortable to wear. The degree of comfort offered by aprotective suit is largely determined by the amount of water vapor thatcan permeate through the protective fabric. The human body continuouslyperspires water vapor as a method for controlling body temperature. Whena protective fabric hinders the loss of water vapor from the body, thetranspirational cooling process is hindered, which leads to personaldiscomfort. When a protective suit allows little or no loss of watervapor, extreme heat stress or heat stroke can result in a short periodof time. Hence, in addition to offering the highest levels of protectionagainst toxic chemicals and liquids, a practical chemical and biologicalprotective suit must have high water vapor transmission rates. Theappropriate protective structure must also be light in weight and offerthe same high level of protection over a long period of time.

There is a large variety of protective apparel available in the markettoday. The garments that offer the highest levels of comfort (high watervapor transmission rates) offer little or no protection against chemicaland biological hazards, while those that offer the highest levels ofprotection against toxic hazards are also typically impermeable to watervapor. For example, garments made from woven fabrics are very breathableand comfortable to wear but offer no protection from noxious agents.Nonwoven fabrics such as those sold under the trade name of Tyvek®spunbonded olefin (available from DuPont, Wilmington, Del.) offerprotection from particulate agents but offer little protection againstchemical liquids and vapors. These nonwoven fabrics are also lesspermeable to water vapor than woven fabrics made from natural or manmadefibers. Protective suits made from multiple layers of laminated polymerfilms offer high level of protection against both liquid and vaporagents but are also largely impermeable to water vapor. Such impermeablesuits may require a Self Contained Breathing Apparatus (SCBA) to providecomfort to the individual wearing the protective suit.

Considerable effort has been expended in creating laminated multilayeredfilm structures for chemical protective apparel. Each layer in thelaminated structure is chosen to impart certain features to the apparel.Some layers provide strength, while others provide resistance tospecific classes of chemicals. Such laminated structures may becharacterized as passive structures because the barrier layersphysically impede the motion of the toxic chemicals without necessarilyinteracting or reacting with the permeating chemical species. U.S. Pat.No. 4,772,510 (Mc Clure), U.S. Pat. No. 4,833,010 (Langley), U.S. Pat.No. 4,855,178 (Langley) and U.S. Pat. No. 5,626,947 (Hauer) describevarious laminated structures consisting of one or more chemical barrierlayers. Such laminated films significantly hinder the permeation ofchemicals, but they also prevent transport of water vapor. Hence,apparel made from such multilayered films is exceedingly uncomfortableto wear.

Another example of a passive protective layer in apparel is the use ofmicroporous membranes. The preparation and characteristics ofmicroporous membranes are well known in the art—see, for example,Richard W. Baker, “Membrane Technology”, in Encyclopedia of PolymerScience and Technology, 3rd Edition, John Wiley & Sons, Hoboken, N.J.,2003, pages 184-248. Such membranes, depending on the pore size and thesurface functionality of the pores, may provide protection againstspecific classes of liquid chemicals. Also, because of the porousstructure, the membrane layer is more breathable and comfortable to wearthan nonporous, multilayered laminated structures. U.S. Pat. No.4,194,041 (Gore) describes the use of a hydrophobic microporous membranemade from either polytetrafluoroethylene or polypropylene in conjunctionwith a hydrophilic polymer layer as a water barrier. U.S. Pat. No.5,260,360 (Mrozinski) describes a microporous membrane made from apolyolefin and a fluorochemical oxazolidinone. However, because thediameter of pores in such membranes typically ranges from 0.1 to 10micrometers, the resulting structure cannot offer much protectionagainst chemical vapors.

Research effort has also been directed towards creating protectiveapparel that is “reactive” in nature. The protective garment is madereactive by encapsulating certain chemical species into the garment thatcan absorb, adsorb or chemically react with toxic chemical vapors asthey diffuse through the garment. Such reactive garments are usuallymade up of multiple layers wherein at least one layer comprises anencapsulated reactant, and at least one outer layer consists of an airpermeable layer. U.S. Pat. No. 4,455,187 (von Blucher) describes the artof creating reactive garments by encapsulating the reactive species inan appropriate polymer and depositing the resulting solids onto a porousfabric. The reactive species suggested in the invention are silicaxerogels, powdered metal oxides and hydroxides, molecular sieves, ionexchangers and various forms of activated carbon. U.S. Pat. No.5,273,814 (Kelly) describes an improved reactive structure for chemicalprotection. The improvement is brought about by the use of a hydrophobicmicroporous membrane layer in conjunction with an activated carbonlayer. The purpose of the microporous membrane is to provide protectionfrom liquid chemicals and to protect the reactive layer from beinginundated and poisoned by liquid chemicals. One of the major limitationsof reactive garments is that they have a limited effective lifetime.This is because the reactive agents such as activated carbon do not justreact with toxic chemical agents but can be poisoned by many differentimpurities in the environment. Thus, the level of protection offered bysuch reactive garments decreases with time. Also, reactive suits thatrely on solid reactants such as activated carbon have significant weightand are therefore cumbersome to wear over long time periods.

Hazardous materials (“hazmat”) protective garments may also be createdfrom semi-permeable or semi-selective polymer membranes. Such membranesare nonporous continuous polymer films usually prepared from polymerelectrolytes and ion exchange polymers. Such selective membranes offersignificant barrier to the permeation of chemical agents but still allowfor the permeation of water vapor. U.S. Pat. No. 4,515,761 (Plotzker)describes the art of creating a composite protective fabric from asemipermeable polymer membrane, which is prepared from a highlyfluorinated ion exchange polymer containing sulfonic acid metal ion saltfunctional groups. U.S. Pat. No. 6,579,948 (Tan) describes a method forcreating protective semipermeable membranes from block copolymers ofpolystyrene and isobutylene, where a fraction of the styrene segmentshave been sulfonated to form sulfonic acid groups. The ionic content ofthe polymer allows for a greater transmission of water vapor than ispossible for membranes made from non-sulfonated styrene blockcopolymers.

There are two major problems with all the protective garments describedin prior art. First, all existing protective garments offer the sameconstant level of protection at all times. In most situations, thewearer of a protective garment does not require protection from theenvironment at all times. Protection is only needed when a toxicchemical or biological agent is present in the environment. Second, noneof the garments described in the art offer an optimum balance ofprotection and comfort. In all cases described so far, either comfort issacrificed at the expense of protection or vice versa. The object ofthis invention is to overcome the aforementioned problems using amembrane structure having movable membranes, one advantage of which is avariable and controllable permeability.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an adaptive membranestructure that includes first and second membranes, and means to respondto an actuating stimulus that moves the first membrane into contact withthe second membrane in a position in which the permeability of thestructure to gas, vapor, liquid and/or particulates is decreased.

Another object of this invention is to provide physical assets anddevices fabricated from or incorporating an adaptive membrane structureas described above including an article of apparel, an enclosure for theoccupancy of humans, animals or a valve for controlling the flow of gasvapor, liquid and/or particulates.

It is a further object of this invention to provide an adaptive membranestructure that includes first and second membranes having holes, andmeans to respond to an actuating stimulus that moves the first membraneinto contact with the second membrane in a position in which the holesof the first membrane are substantially out of registration, or are outof registration, with the holes of the second membrane.

Yet another object of this invention is to provide an adaptive membranestructure that includes first and second membranes having holes, andmeans to respond to an actuating stimulus that moves one or moreportions of the first membrane into contact with a corresponding portionor portions of the second membrane in a position in which the holes ofeach portion of the first membrane are substantially out ofregistration, or are out of registration, with the holes of thecorresponding portion of the second membrane.

Yet another object of this invention is to provide an adaptive membranestructure that includes first and second movable membranes, and means torespond to an electrical force, a magnetic force, a hydrodynamic forceor a hydrostatic force.

Yet another object of this invention is to provide, in a membranestructure comprising first and second movable membranes, a method formoving the first membrane toward the second membrane by applying anelectrical force, a magnetic force, a hydrodynamic force or ahydrostatic force to the first membrane.

Yet another object of this invention is to provide a method forcontrolling the flow of gas, vapor, liquid and/or particulates throughfirst and second membranes having holes, by (a) providing the holes ineach membrane in a position in which, when the membranes are in contactwith each other, the holes are substantially out of registration, or areout of registration, and (b) moving the membranes into contact with eachother.

Yet another object of this invention is to provide an adaptive membranestructure that includes first and second movable membranes having holes,and a spacer located between the membranes that does not block any hole.Further included, if desired, may be means for deforming one of themembranes to move it into contact with the other membrane.

Yet another object of this invention is to provide an adaptive membranestructure that includes first and second movable membranes, means torespond to an actuating stimulus that moves the first membrane intocontact with the second membrane, and a sensor that activates theactuating stimulus.

Yet another object of this invention is to provide an adaptive membranestructure that includes A first membrane having holes, a second membranehaving protruding members, and means responsive to an actuating stimulusthat moves one membrane toward the other membrane, wherein theprotruding members are positioned on the second membrane to beinsertable in the holes on the first membrane when one membrane is movedtoward the other.

The invention also provides a process for fabricating adaptive membranestructures.

Other objects and advantageous technical effects offered by thisinvention are more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an unactuated adaptive membranestructure, indicating high permeability. (1A: perspective view. 1B: planview. 1C: sectional view.)

FIG. 2 is a schematic diagram of an adaptive membrane structure in itsactuated state, illustrating the lack of registration of holes onadjacent membrane layers. (2A: perspective view. 2B: plan view. 2C:sectional view.)

FIG. 3 is a schematic diagram of a section view of a membrane with ahole of non-circular cross-section.

FIG. 4 is a schematic diagram of an unactuated adaptive membranestructure comprising a pair of adjacent membranes, each outer surfacecoated with a conducting layer. (4A: perspective view. 4B: plan view.4C: sectional view.)

FIG. 5 is a schematic diagram of the adaptive membrane structure systemof FIG. 4 as actuated. (5A: perspective view. (5B: plan view. 5C:sectional view.)

FIG. 6 is a schematic diagram of an adaptive membrane structure in whichconductive layers are coated with dielectric material. (6A: perspectiveview. 6B: plan view. 6C: sectional view.)

FIG. 7 is a schematic diagram of a sectional view of alternativeconfigurations of an adaptive membrane structure comprising twosubstrate membranes, two conductive layers, and two dielectric coatings.

FIG. 8 is a schematic diagram of a substrate membrane of an adaptivemembrane structure in which a conductive layer is applied to thesubstrate membrane in an annular pattern around each hole.

FIG. 9 is a schematic diagram of a substrate membrane of an adaptivemembrane structure in which a conductive layer is applied to thesubstrate membrane in parallel lines.

FIG. 10 is a schematic diagram of a portion of a substrate membrane ofan adaptive membrane structure in which a patterned dielectric layer isapplied to a patterned electrode layer applied to a substrate membrane.

FIG. 11 is a schematic diagram of an adaptive membrane structurecomprising three substrate membranes, three conductive layers, and threedielectric layers. (11A: perspective view. 11B: plan view. 11C:sectional view.)

FIG. 12 is a schematic diagram showing a sectional view of threepossible states of actuation of an adaptive membrane structurecomprising three substrate membranes, three conductive layers, and threedielectric layers.

FIG. 13 is a schematic diagram of an unactuated adaptive membranestructure that includes a spacer material as a deactuation means. (13A:perspective view. 13B: plan view. 13C: sectional view.)

FIG. 14 is a schematic diagram of an actuated adaptive membranestructure that includes a spacer material as a deactuation means. (14A:perspective view. 14B: plan view. 14C: sectional view.)

FIG. 15 is a schematic diagram of an adaptive membrane structurecomprising an array of protruding features, in the unactuated state(15A: perspective view. 15B: sectional view.).

FIG. 16 is a schematic diagram of an adaptive membrane structurecomprising an array of protruding features, in the actuated state (16A:perspective view. 16B: sectional view.)

FIG. 17 is a schematic diagram of the cell used in measuring the oxygenpermeability of the adaptive membrane structures (17A perspective, 17Bsection).

FIG. 18 is a graph of the O₂ concentration in the low concentration sideof the test cell for an adaptive membrane structure in actuated (voltageon) and unactuated states (Example 2).

FIG. 19 is a schematic diagram of an exploded view of an adaptivemembrane structure containing four membranes and three spacers, asdescribed in Example 4.

FIG. 20 shows a plan view of an adaptive membrane structure that hasfour subsections and each subsection has an array of holes.

DETAILED DESCRIPTION OF THE INVENTION

One important object of this invention is to overcome the aforementionedlimitations of protective garments and other protective structures byproviding an adaptive membrane structure. An “adaptive membranestructure” is a structure comprising at least two membranes wherein themembranes are movable upon the activation or application of an actuatingstimulus such as a force. The membrane structure is thus “adaptive” inthe sense that the permeability of the structure can be changed based onthe conditions in the external environment.

A “membrane” as used in this invention is a discrete, thin structurethat moderates the transport of species in contact with it, such as gas,vapor, aerosol, liquid and/or particulates. Examples of membranesinclude without limitation film, plastic sheeting, synthetic barriers,layers, laminar structures, woven fabric, and nonwoven sheet. A membranemay be chemically or physically homogeneous or heterogeneous. A“microporous membrane” is a membrane typically containing pores in therange of 0.1 to 10 micrometers in diameter. Microporous membranes aretypically characterized by the fraction of total membrane volume that isporous (i.e. relating to porosity), a term reflecting the average porelength within the membrane compared with membrane thickness (i.e.relating to tortuosity), and average pore diameter. The term “pore” asused herein denotes an opening that exists in a membrane that may or maynot completely traverse the membrane. Typically, the pore size, the poreshape and/or the pore placement is not well defined or controlled,though there may be a relatively reproducible average pore size and/orpore size distribution.

The membranes used in the structure of this invention typically haveholes as distinguished from pores, a “hole” being an opening thatcompletely traverses a membrane. The holes of one membrane may or maynot be the same size and shape as the holes of another membrane.Although holes are described herein in terms of their having the shapeof a circle, it is not required that a hole have a shape that isperfectly or even approximately circular.

The holes of one membrane may be aligned with the holes of anothermembrane, in the vertical sense of a line perpendicular or essentiallyperpendicular to the respective planes of the membranes, such that theholes overlap completely, partially or not at all. Holes overlapcompletely when, if they are the same size, their boundaries arecoincident in vertical alignment, or if they are not the same size, thearea of the smaller hole fits entirely within the area of the largerhole. Holes do not overlap at all when, again in the sense of verticalalignment, a line perpendicular or essentially perpendicular to therespective planes of the membranes that passes through a hole on onemembrane does not pass through any part of a hole on the other membrane.Membranes that have no overlap are shown in FIGS. 1C and 2C. Partialoverlap is the intermediate condition when the perpendicular oressentially perpendicular line passing through a hole on one membranewill pass through only a portion of a hole on the other membrane.

The term “open area” is used to refer to the extent, expressed as apercentage, to which the respective holes of two membranes overlap. Formembranes that do not overlap at all, such as those of FIGS. 1C and 2C,the open area is defined as 0%. Conversely, an open area of 100%corresponds to the existence of the maximum open area, which isachievable by arranging a particular set of membranes such that theholes completely overlap. A percentage between 0 and 100 indicatespartial overlap. The terms “not in registration” and, equivalently, “outof registration” are used herein to indicate that the holes in twomembranes do not overlap at all (referring again, for example, to FIGS.1C and 2C); this is equivalent to having an open area of 0. The term“substantially out of registration” indicates that there is partialoverlap, i.e. that the open area of the membrane structure is in therange of from greater than 0% up to, but not including, 50%.

The adaptive membrane structure of this invention may be “actuated”,which denotes the state of the structure upon the application oroperation of a stimulus, such as a force (the “actuating stimulus”),which causes surfaces of adjacent membranes to move into contact witheach other, thereby changing the permeability of the membrane structure.Adjacent membranes are membranes that may be brought into contact witheach other. The term “unactuated” thus denotes the state of the adaptivemembrane structure before application of the actuating stimulus, inwhich state a gap exists between the membranes that will be brought intocontact upon application of the actuating stimulus. The term“deactuated” denotes the state of the adaptive membrane structure afterthe application and subsequent removal of the actuating stimulus whenaccompanied by re-formation of the gap between adjacent membranes thathad been in contact when actuated.

The term “adaptive barrier system” as used herein denotes a systemcomprising an adaptive membrane structure in which actuation changes thepermeability of the membrane structure to chemical, biological and/orparticulate species.

Thus, the adaptive membrane structure of this invention is capable ofdisplaying a variety of states of gas, vapor, liquid and/or particulatepermeability. For example, when the membrane structure of this inventionis used for protection against hazardous agents, it can display twodifferent states of permeability. In one state, when hazardousenvironmental conditions do not exist, the membrane structure of thisinvention is highly permeable to water vapor and gases, thereby offeringa high level of personal comfort. The term “unactuated” is used hereinto denote this state. When the membrane structure of this invention isexposed to a hazardous environment, it is transformed to another state,in which it is impermeable to hazardous chemical and/or biologicaltoxins and/or pathogens, thereby offering a high level of protectionwhen it is needed. In the actuated state, the structure may, however,remain permeable to water vapor.

The conversion of the membrane of this invention from one state ofpermeability to another state of permeability is brought about by theapplication of a stimulus, such as a force, herein termed an “actuatingstimulus”. The actuating stimulus can be any of several forms includingwithout limitation pressure, force, change in temperature or ambientconcentration of water vapor, voltage, current, magnetic field, andelectric field. In one embodiment of this invention, the actuatingstimulus takes the form of an applied electric field, which causesmembranes within the structure to move to convert the structure from anunactuated to an actuated state.

The application of the actuating stimulus could be effected with amanually operated switch. In an alternative embodiment, however, asensor could detect a change in the environment in which the structureis located, and could automatically activate the actuating stimulus. Thesensor could do this by responding, for example, to a change intemperature or humidity or to the presence (as indicated by change ofconcentration) of an undesirable chemical, biological and/or particulatespecies by sending a signal (for example, an electrical, optical orradio wave signal) to close a circuit to activate, i.e. trigger theapplication of, the actuating stimulus.

A schematic of a typical embodiment of the adaptive barrier system ofthis invention is shown in FIGS. 1A, 1B and 1C. The system comprises apair of planar membranes 2 and 2′ that are largely parallel to eachother, each membrane further comprising a geometric array of holes suchas those denoted 3 and 3′ in FIGS. 1A, 1B and 1C. The holes completelytraverse the thickness of the membranes, giving rise to a path ofincreased convection and/or diffusion of a chemical, biological and/orparticulate species across and through the membrane thickness whencompared to convection and/or diffusion of the same species through themembrane material surrounding the hole. When the adaptive barrier systemis not actuated, the adjacent surfaces 4 and 4′ of the membrane pair 2and 2′ are not in contact with each other, such that a gap 5 existsbetween membranes 2 and 2′. When an actuating force is applied to theadaptive barrier system, it moves one or both of the membranes 2 and 2′the surfaces 4 and 4′ of which are brought in contact with each other,thus eliminating the gap between 2 and 2′, as shown in FIGS. 2A, 2B and2C.

It is a further characteristic of the invention that the array of holesin each membrane is such that the openings of the array of holes on theadjacent membrane surfaces 4 and 4′ are typically at least substantiallyout of registration with each other. That is, when the adaptive barriersystem is actuated, the degree of hole overlap is such that the openarea is reduced to less than 50%. It is preferred that the open area bereduced to 10% or less, and more preferred that it be reduced to 1% orless upon actuation. In a further preferred embodiment, the holes areout of registration, and the open area is reduced to 0% upon actuation.In this most preferred embodiment of the present invention, no holeopening on the surface 4 of the membrane 2 will overlap with a holeopening on the adjacent surface 4′ of the membrane 2′. When the twoadjacent membranes 2 and 2′ are in contact, the holes of each membraneare therefore effectively sealed. There is consequently no continuousporous path for convection and/or diffusion of chemical, biologicaland/or other particulate species across two adjacent membranes incontact, as seen in FIG. 2C. However, when the two adjacent membranesurfaces 4 and 4′ are not in contact, chemical, biological and/or otherparticulate species may traverse one membrane through its holes, enterthe gap between the non-contacting membranes, and then traverse thesecond membrane through its holes (see, e.g., flow path 6 in FIG. 1C).Convection and/or diffusion of species will be greatly enhanced throughadjacent membranes that are not in contact as compared to convectionand/or diffusion of the same species when the same adjacent membraneshave been moved into contact through action of the actuating force.

As noted above, although the holes depicted in FIGS. 1A, 1B, 1C, 2A, 2Band 2C are right circular cylindrical holes with linear axes normal tothe plane of the membranes, the holes of the invention are not limitedto this geometry. In particular, each hole may have other non-circularcross-sectional shapes and/or inclinations of their axes relative to theplane of the membrane. Indeed, generally, it is not required that anyhole traverse the membrane along a linear path but may instead follow anon-linear, tortuous path. Furthermore, the cross-sectional shape of anyhole need not be constant as the hole traverses the membrane. FIG. 3shows a section view of part of a membrane according to the inventionwith a hole with non-circular cross-section, which changes in shape andsize as it traverses the membrane along a general tortuous path. Theoptimum hole diameter will vary depending on the specific use to be madeof the adaptive membrane structure, particularly how much flow ordiffusion is desired through holes in the unactuated state. In allcases, the holes must be large enough to allow transport to occur in theunactuated state.

Although the hole arrays depicted in FIGS. 1A, 1B, 1C, 2A, 2B and 2Ccomprise the same regular square pitch pattern, the hole arrays of thisinvention are not limited to this pattern. In particular, the arraypattern on membrane 2 may be different from the pattern on membrane 2′,and either pattern may comprise any regular or non-regular pitch patternprovided that the patterns are such that upon contact of the pair ofadjacent surfaces 4 and 4′ under action of the actuating force, theholes on the surface 4 of the membrane 2 will be at least substantiallyout of registration, if not out of registration, with the opening of anyhole on the adjacent surface 4′ of the membrane 2′.

Again referring to FIGS. 1A, 1B, 1C, 2A, 2B and 2C, the membranes 2 and2′ may be fabricated from the same or different materials orcombinations of materials and, furthermore, each membrane of the pairmay have the same or different thickness. The materials from which themembranes are fabricated are selected to impart desirable levels ofpermeability to one or more species, which may come in contact with themembrane in use. For example, the material comprising the membrane maybe selected to have high permeability to water vapor but very lowpermeability to one or more human toxic or poison agents or pathogens asmay be encountered by military personnel subjected to a chemical warfareattack.

The materials that may be used to create membranes 2 and 2′ can bechosen from any sheet structure, but it is preferred that the sheetstructure be flexible, and it is also preferred, although not necessary,that the materials used are polymeric in nature. Preferably, theflexible sheet structure may be prepared from at least one polymercomponent. Such polymer sheets or films, used to create membranes 2 and2′, may be continuous (i.e. containing no microvoids or micropores) ormicroporous. Methods for creating polymer sheets or films are well knownin the art. Such polymer sheets or films can be prepared from a largevariety of polymers. Polymers that may be used for creating sheets orfilms include without limitation polyesters, polyolefins (especiallyhigh-performance polyethylene), polyamides (aliphatic, aromatic, andmixed aliphatic/aromatic), polybenzazoles, polyimides,polyacrylonitrile, polysulfones, polycarbonates, homopolymer andcopolymers of tetrafluoroethylene, homopolymer and copolymers ofvinylidene difluoride, copolymers of butadiene and styrene, copolymersof ethylene and vinyl acetate, copolymers of ethylene and vinyl alcohol,copolymers of ethylene and acrylic monomers such as methacrylic acid andacrylic acid, and ionomers. Nonlimiting examples of suitable ionomersinclude ionomers formed by neutralizing copolymers of ethylene acidcopolymers, perfluorinated sulfonate and carboxylate ionomers, andsulfonated polystryrene.

Polymer films and sheets produced from thermoplastic and vulcanizedelastomers such as, but not limited to, polyurethanes, block copolymersand random copolymers of styrene and butadiene, block copolymers andrandom copolymers of styrene and isoprene, homopolymers of butadiene andisoprene, copolymers of ethylene and propylene, fluoroelastomers,natural rubbers, nitrile rubbers, polyacrylate rubbers, butyl rubbersand silicone rubbers are also useful as membrane materials in thepresent invention.

Continuous polymer films to be used to create membranes 2 and 2′ mayalso be semipermeable in nature. Semipermeable polymer membranes andtheir manufacture are known, for example, from sources such as U.S. Pat.No. 4,515,761 (Plotzker) and U.S. Pat. No. 6,579,948 (Tan).

The starting materials to create the membranes used in the presentinvention are not limited to continuous polymer films. Suitable startingmaterials may also have microvoids or micropores such as those presentin microporous membranes, in which the typical pore size is about 0.1 to10 micrometers. Various methods for creating microporous membranesinclude

-   -   the track-etch process used for creating Nuclepore® brand        polyester and polycarbonate membranes (Whatman Inc., Clifton,        N.J.);    -   phase inversion processes for creating polysulfone, aromatic        polyamide, and polyvinylidene fluoride membranes;    -   stretching processes for creating microporous        polytetrafluoroethylene and polyethylene membranes;    -   phase separation processes in which a nonreactive species        (“porogen”) present during a polymerization reaction is        subsequently extracted from the polymer product; and    -   spun bonded/melt blown processes for creating nonwoven sheet        structures.

The membrane may also contain materials to adsorb, absorb or react withharmful and undesired species. Hence, the membrane may include activatedcarbon, high surface silica, molecular sieves, xerogels, ion exchangematerials, powdered metal oxides, powdered metal hydroxides,antimicrobial agents, and the like, which may be in the form ofnanoparticles if so desired. Such materials would typically be mixedinto the membrane material during the membrane formation process, suchas, which might include a process such as extrusion compounding orsolution casting.

Holes, for the adaptive membrane structures of this invention, may beformed by any hole manufacturing process known in the art. Mechanicalprocesses that may be used for creating holes in sheets and filmsinclude without limitation drilling, punching, piercing, boring andperforating. Holes may also be created by other methods such asultrasonic waves, electrical discharge, high energy radiation such aslasers and electron beams, and high velocity water jets. Various etchingtechniques, whereby material is removed by chemical means, may also beused to create holes for this invention. A preferred hole manufacturingprocess for this invention is one in which material occupying the spacewhere the hole is to be created is removed with the least amount ofdistortion to the material surrounding the hole. Methods for holemanufacturing that are especially preferred are mechanical punching andlaser or electron beam drilling. Once the holes have been created, themembranes of this invention may be further processed to reduce anysurface distortion that may have resulted due to hole formation process.Processes that may be used include without limitation calendaring,pressing and planishing.

A preferred actuating stimulus for use in this invention is the forceproduced by electrostatics. The preferred electrostatic force may beapplied to the system by incorporating electrically conducting materialsin or onto specific regions of at least two and possibly more membranessuch that upon action of appropriate circuitry, the conducting regionson at least two membranes become oppositely charged, thereby creating anattractive force which brings two adjacent membranes into contact. Inone embodiment, therefore, means to respond to an actuating stimulus mayinclude such electrically conducting materials, and the features, linesand patterns into which they may be formed, on which an electrostaticforce may operate.

FIGS. 4A, 4B and 4C show schematically a particular embodiment of a pairof adjacent membranes 2 and 2′ configured for an electrostatic actuatingforce. In this case, the surface of each membrane that is not adjacentto gap 5, which separates the membranes, is coated with a conductinglayer 7 and 7′. As the adaptive membrane structure of this invention maycontain one or more membranes and/or layers in addition to the twomembranes that are brought into contact by the actuating stimulus, it isnot required in this embodiment that more than two membranes have aconductive coating, or that the membranes that have a conductive coatingare the membranes that are brought into contact. That is, layers and/orother membranes may be interposed between the membranes with holes thatcome into contact and the place where direct application of theactuating stimulus occurs. Whatever is required to make the membraneswith holes move is, however, part of the adaptive membrane structure,and the permeability of the structure is thus determined with respectall such components, be they just the two membranes with holes oradditional layers, membranes and/or other materials or components.

Possible metallic conductive coatings may include without limitationsilver, aluminum, copper, nickel, palladium, platinum, gold and alloysof these metals. An electrically conductive coating may also be preparedby dispersing colloidal forms of the aforementioned or other conductivemetals into various polymers. Electrically conductive layers orelectrodes may also be prepared from carbon black, graphite, carbonnanotubes, fullerenes and dispersions of such forms of carbon intopolymers. Additional forms of conductive layers or electrodes includethose, which may be formed from indium tin oxide or from polymers thatare inherently electrically conducting. Electrically conducting polymersinclude without limitation polyacetylene, polyaniline, polythiophenes,polypyrrole, poly(p-phenylene), poly(p-phenylene vinylene) or suchconductive polymers that have been chemically modified, for example,with dopants to increase conductivity. The conducting layers 7 and 7′may comprise the same or different materials and thickness.

As depicted in FIGS. 4A and 4C, the two coated layers on the adjacentmembranes are connected in series with each other through conductors 8to a switch 9 and a source of electrical potential 10 which may includea battery or other power source such as a solar panel or fuel cell. Asshown in FIGS. 4A and 4C, when the switch is open, there is noelectromotive force and thus no actuating stimulus. As shown in FIGS. 5Aand 5C, however, when the switch is closed, an attractive electrostaticforce develops between the membranes and thereby brings the membranesinto contact along their adjacent surfaces.

For example, an adaptive membrane structure may be fabricated by aprocess of (i) providing at least two membranes, each independentlycomprising a flexible sheet, film, microporous membrane, or nonwovenlayer; each membrane containing an array of holes, (ii) assembling themembranes parallel to each other such that the holes in adjacentmembranes are substantially out of registration or are out ofregistration, and (iii) providing a means responsive to an actuatingstimulus to the assembled membranes. In addition, an electricallyconductive layer may be applied to one side of each of at least two ofthe membranes, and the electrically conductive layers may be attached toa voltage source and a switch. The holes may be made by at least onemethod selected from among mechanical drilling, punching, piercing,boring, perforating, drilling with ultrasonic waves, drilling byelectrical discharge, laser drilling, electron beam drilling, anddrilling with high velocity water jets.

Additionally, as shown for example in FIGS. 6A, 6B and 6C, theconductive layers 7 and 7′ on each membrane may be coated with one ormore dielectric layers 11 and 11′, which can impart additional featuresto the membrane structure. In particular, these layers may serve toinsulate the conductive layers 7 and 7′ from the environment therebyeliminating or minimizing the potential for undesirable shorting orarcing of the charged conductive layer to surrounding conductiveobjects. The dielectric layers 11 and 11′ may comprise the same ordifferent materials and thickness. Furthermore, in general, thedielectric layers 11 and 11′ may be the same material or a differentmaterial than that comprising the substrate membranes 2 and 2′. Notefurther that a dielectric layer may be installed on the side of membranethat will be brought into contact with another membrane, or on theopposite side. For example, in FIGS. 6A and 6C, dielectric layer 11 ison the side of membrane 2, and dielectric layer 11′ is on the side ofmembrane 2′, that will be brought into contact with each other. Thecontact in this situation will actually be between the two dielectriclayers 11 and 11′. In the embodiment shown in FIG. 7A, however, contactwill be made by membrane 2 on the side opposite from layer 11, and inthe embodiment shown in FIG. 7B, contact will be made by each membraneon the side opposite from which the dielectric layer is installed.

In those cases where the dielectric layer is positioned to face theadjacent membrane as in FIGS. 6C and 7A, an added function of thedielectric layer may be to enhance the seal formed when the membranescome in contact as a result of application of the actuating stimulus. Inparticular, as described in the examples below, a coating comprising acompliant dielectric material such as an elastomer is especially suitedto provide a compliant surface to enhance sealing of the membranesurfaces in contact under action of the actuating stimulus. Suchelastomers include without limitation polyurethanes, polyurethane-ureas,thermoplastic and vulcanized forms of styrene butadiene and styreneisoprene rubbers, natural rubber, silicone rubbers, butadiene rubbers,ethylene propylene rubbers, acrylic rubbers, and fluoroelastomers.

In certain embodiments, a conductive layer 7, and a dielectric layer 11if present, may be installed on the side of a membrane 2 that will notcome into contact with another membrane 2′. This embodiment is shown inFIG. 7B. In this kind of embodiment, it is preferred that the holes 3,in addition to fully penetrating the substrate membranes 2 and 2′, alsofully penetrate conductive layers 7 and 7′ and also fully penetrate thedielectric layers 11 and 11′. It is not required, however, that in suchcase the holes 3 fully penetrate the conductive and dielectric layers,and either or both of those layers may instead cover the entire surfaceof that side of the membrane 2 and/or 2′. In such case, the permeabilityof the conductive and/or dielectric layer can influence the overallpermeability of the membrane structure to the passage of the chemical,biological and/or other particulate species for which the system isdesigned.

Yet another function of the dielectric layer may be to adsorb, absorb,or react with harmful and undesired species that may diffuse into themembrane structure when the membrane is in the unactuated state. Hence,the dielectric layer may include activated carbon, high surface silica,molecular sieves, xerogels, ion exchange materials, powdered metaloxides, powdered metal hydroxides, antimicrobial agents, and the like,which may be in the form of nanoparticles if so desired.

Alternatively, the conducting layers need not cover the entire surfaceof a substrate membrane but instead may be selectively applied in apattern, which only partially covers the substrate membrane surface. Onesuch example is shown in FIG. 8, in which a conductive layer 7 isapplied to a substrate membrane 2 in an annular pattern around each hole3. All the annuli are connected to each other using electricallyconducting lines applied to the substrate membrane 2 such that all theannular patterns are electrically connected to each other in series sothat all annuli can be held at the same electrical potential byappropriate connection to a voltage source at some point in the networkof lines and annuli. Another possible patterned electrode is shown inFIG. 9, in which the conducting layer 7 comprises two arrays of parallelelectrically conducting lines applied to the substrate membrane 2traversing the space between the holes. In the particular pattern shownin FIG. 9, it is seen that any line from either array intersects and isperpendicular to the lines in the other array. Again, all points in thisnetwork of lines may be held at a single electrical potential byappropriate connection to a voltage source. The use of a patternedconducting layer as shown in FIGS. 8 and 9, as opposed to a continuouselectrode as shown in FIG. 4, can increase the desirable permeability ofthe structure in the actuated state to species such as water vapor,since the barrier afforded by the electrode material to transport ofthese desirable species is removed over much of the substrate membranesurface. There are many other geometric patterns that could be used toprovide electrodes in this invention.

The method for laying down conductive features, lines and patterns ontosurfaces is well known in the electronic manufacturing art. Some of theprocesses that may be used for creating conductive features includewithout limitation letterpress printing, screen printing, gravureprinting, offset lithography, flexography, electrophotography and laserjet printing. Several additional variations of lithographic printing forlaying down micron and submicron conductive features onto surfaces arealso well known in the art.

Dielectric layers, if they are incorporated in the structure asdescribed above, also need not cover the entire surface of the substratemembrane. In particular, if a patterned electrode is used in a structureof this invention, a patterned dielectric layer may be used which coversthe patterned electrodes to electrically isolate them from theirsurroundings, but the dielectric layer need not cover all of theremaining substrate surface, which is not covered by the patternedelectrode layer. FIG. 10 shows an example of a patterned dielectriclayer 11 applied to a patterned electrode layer 7 applied to a substratemembrane 2 in a similar design. It will be noted that the patterneddielectric in this example covers an area slightly larger than thepatterned electrode to insure isolation of the electrode. Note that thepatterned dielectric layer may also have functions in addition toelectrical isolation as described above for dielectric layers that coverthe entire substrate surface. In particular, it may serve to enhance thesealing of the membrane surface to the adjacent membrane surface. Theaforementioned processes for patterning conductive layers may also beused to pattern dielectric layers onto membrane substrates of thisinvention.

This invention is not limited to adaptive membrane structures havingonly two substrate membranes. For example, FIGS. 11A, 11B and 11C showan adaptive membrane structure comprising three substrate membranes 2,2′ and 2″. Since, in this embodiment, the means responsive to theactuating stimulus again includes one or more electrical conductors,conducting layers 7, 7′ and 7″ and associated dielectric layers 11, 11′and 11″, as well as their associated array of holes, are shown inaddition to substrate membranes 2, 2′ and 2″. The openings of the arrayof holes on membrane 2 in relation to the holes of membrane 2′ are shownto be out of registration, and the openings of the array of holes onmembrane 2′ in relation to the holes of membrane 2″ are shown to be outof registration. As noted above, however, the openings of the array ofholes on membrane 2 in relation to the holes of membrane 2′, and theopenings of the array of holes on membrane 2′ in relation to the holesof membrane 2″, could, either or both, be substantially out ofregistration instead of out of registration.

Two potential sources 10 and 10′, switches 9 and 9′, and conductors 8are provided to permit electrostatic actuation of the conductors in thesystem. Thus, three different actuation states can be achieved with thissystem. As shown in FIG. 12A, the upper and middle membranes may bebrought in contact and only their associated holes sealed by closure ofswitch 9. Or, as shown in FIG. 12B, the middle and lower membranes maybe brought in contact and only their associated holes sealed by closureof switch 9′. Or, as shown in FIG. 12C, the upper and middle as well asthe middle and lower membranes may be brought in contact and all holesmay be sealed by closure of both switches 9 and 9′.

Note that the materials and thickness of substrate membranes 2, 2′ and2″ may be the same or different. Likewise, the materials and thicknessof conducting layers 7, 7′, and 7″ may be the same or different.Likewise, the materials and thickness of the dielectric layers 11, 11′,and 11″ may be the same or different. Furthermore, the choice of whichside of the substrate membrane to use for placement of the dielectriclayer, for any or all of the three membranes, may be reversed aspreviously disclosed above.

The design disclosed in FIGS. 11A, 11B and 11C may be extended to fouror more membranes as well by addition of appropriate component substratemembranes, conducting layers, dielectric layers, hole arrays, potentialsources, switches and conductors. Furthermore, the conducting anddielectric layers may cover the entire substrate membrane surface towhich they are applied or they may be patterned following, for example,the designs previously disclosed. Multiple membrane systems enableadaptive barrier systems, which can selectively impede the passage ofdifferent chemical, biological and/or other particulate species byactuating different combinations of adjacent membrane closures. Suchsystems may include, in addition to one or membranes in addition to twothat are brought into contact, one or more layers of fabric.

The embodiments disclosed above may thus include, for example, inaddition to first and second membranes (2 and 2′), a third membrane 2″having holes, and means to respond to an actuating stimulus that movesthe third membrane into contact with the second membrane in a positionin which the holes of the third membrane are substantially out ofregistration with, or are out of registration with, the holes of thesecond membrane. The structure may also include third and/or fourthmembranes (2″ and 2′″) having holes, and means to respond to anactuating stimulus that moves the third membrane into contact with thesecond and/or fourth membrane in a position in which the holes of thethird membrane are substantially out of registration with, or are out ofregistration with, the holes of the second and/or fourth membranes.

Although an applied electric field is a preferred form in which theactuating stimulus will operate, there are numerous other types ofactuating stimuli that are useful for the purpose of causing themovement of membranes in the structure of this invention. Other possibleactuating stimuli include without limitation a magnetic force,hydrostatic force, or hydrodynamic force, and two or more differentkinds of actuating stimuli may be used on a membrane structure.

For example, certain polymers can absorb considerable amounts of waterand other solvents, and can thereby swell to volumes that aresignificantly greater than the original dry volume. In so doing, theexpansion and change of dimension of such a swellable polymer cantransmit a hydrostatic force that would cause membrane movement.

Changes in temperature can also serve as another form of an actuatingstimulus. Certain synthetic materials, naturally-occurring materials andengineered structures can generate significant forces as they changetheir dimensions in response to changes in temperature. Such a gain orloss of thermal energy may thus also be used to cause the movement ofmembranes herein, working through the material as its size is changedthereby.

In another embodiment, an electrostrictive material may be used totransmit a force derived electrically. An electrostrictive material,when subjected to electrical voltage, can undergo size deformation, witha consequent change in dimension, which can produce a force that willtransmit the effect of the actuating electrical stimulus and move amembrane.

An embodiment based on the use of a magnetic force as the actuatingstimulus can be configured by incorporating a spiral or helical windingof a conducting wire (e.g. copper wire) in the adaptive membranestructure so that the winding is adjacent to the membranes in thestructure and oriented such that the axis of the winding is normal tothe plane of the membranes. The winding is electrically connected inseries with a switch and a source of electrical power such as a battery.A magnetic material is incorporated in one or more of the membranes inthe structure, and the membranes are appropriately located within thestructure such that their motion under action of the force of magneticattraction will cause them to come in contact with each other or withone or more other adjacent membranes. The magnetic material could beincorporated within the bulk of a membrane or as a coating on a membranesurface. Possible magnetic materials include carbonyl iron particlesdispersed within the bulk of a membrane or within a matrix comprising acoating on a membrane surface. Upon actuation of the system by closureof the switch, a magnetic field will develop in the vicinity of thewinding, and this field will generate a force on the magnetic materialincorporated in one or more membranes thereby causing the membrane(s)containing the magnetic materials to come in contact with one or moreadjacent membranes.

The examples discussed above also illustrate a corresponding variety inthe means that is provided to respond to the actuating stimulus,examples of which included above are a swellable polymer, a materialthat changes size in response to temperature change, an electrostrictivematerial and a magnetic material. Also suitable for use as meansresponsive to an actuating stimulus is a thermoelectric material, whichcan generate electrical energy when subjected to a change intemperature, and thus transmit to membranes the force a useful voltagethat is representative of a gain in thermal energy.

The means responsive to the actuating stimulus are typically located in,on, within or adjacent to the adaptive membrane structure in the sensethat they must be in close enough physical proximity to enableapplication of the force of the actuating stimulus to move at least onemembrane. A conductor or magnetic particles may, for example, be printedon a membrane that has holes, may be printed on another membrane orlayer that does not have holes, or may be formed itself as a separatemembrane or layer. Further, a polymer or layer that changes shape and/orsize may be located adjacent to a membrane that has holes, althoughother membranes or layers that do not have holes may be locatedtherebetween provided that the mission of the polymer or material toapply a moving force to the membrane with holes is not hindered.

In view of the variety of forms in which the actuating stimulus mayexist, as described above, another aspect of this invention is anadaptive membrane structure that includes first and second movablemembranes, and means to respond to an electrical, a magnetic, ahydrodynamic or a hydrostatic force. This also enables, in a membranestructure that includes first and second movable membranes, a method formoving the first membrane toward the second membrane by applying anelectrical force, a magnetic, a hydrodynamic or a hydrostatic force tothe first membrane.

Whatever form the actuating stimulus takes, it operates in oneembodiment to a substantially uniform extent on all portions of at leastone membrane. In particular in this embodiment, the actuating stimulusoperates to a substantially uniform extent on the portion of a membraneproximal to each of the holes thereof, and thus in a regular pattern allacross the surface of the membrane. The operation of the actuatingstimulus is only substantially uniform because the membrane is pliableand will in many cases not form a perfect plane on which the appliedforce may operate equally on all infinitely small units of area acrossthe surface of the plane. The intention in such case, however, is thatthe entire membrane move as a result of the application of the actuatingstimulus.

In another embodiment, however, the actuating stimulus does not operateto a uniform extent on all portions of the membrane, and one or moreportions of one membrane are moved into contact with a correspondingportion or portions of another membrane in a position in which the holesof each portion of the first membrane are substantially out ofregistration, or are out of registration, with the holes of thecorresponding portion of the second membrane. If there is more than oneportion of the membrane where contact is made, the portions may, butneed not, be selected in the form of regularly repeating geometricpattern. When the portions are distributed across the surface of themembrane in a regular pattern, it then becomes possible to regulate thepermeability of the membrane structure by arranging for the actuatingstimulus to be operative in only certain selected portions of themembrane at one time. It also becomes possible to rotate the applicationof the actuating stimulus, in a repeating sequence of actuation anddeactuation, among the various portions on a programmed basis. This ismost easily accomplished where an electrical force is the actuatingstimulus, and circuity is provided that enables current to be suppliedto or withdrawn from portions of the membrane with whatever spatial andtiming arrangement is desired.

In particular, the adaptive membrane structure of this invention can bedesigned to display multiple states of gas, vapor and/or liquidpermeability in addition to and different from those exhibited when theadaptive membrane structure is in the fully actuated, fully unactuatedor fully deactuated state. In one embodiment, an adaptive membranestructure may be formed to have two or more portions or subsections,where each subsection of the structure is itself an adaptive membranestructure that displays some or all the features described herein. Thepermeability of the structure as a whole may be altered by changing thepermeability of some or all of the subsections of the structure, and bydoing so at different times. An actuating stimulus can be applied toeach subsection of the membrane structure independently of all the othersubsections. Hence, several different states of permeability may beobtained for the structure as a whole by moving membranes in some of thesubsections, while not moving membranes in other of the subsections,that together make up the adaptive membrane structure as a whole. Inanother embodiment, however, all membranes in all subsections may bemoved at the same time.

One example of an adaptive membrane structure that has several suchsubsections is illustrated in FIG. 20. The figure shows a plan view of amembrane that has four subsections, and each subsection consists of anarray of holes. Two or more membranes such as the membrane illustratedin FIG. 20 can be provided in the structure such that the array of holesin each subsection of one membrane are substantially out ofregistration, or are out of registration, with the array of holes of thecorresponding subsection on another adjacent membrane. A separateactuating stimulus, and means responsive thereto, can be provided foreach subsection of a membrane. For example, in an embodiment where theactuating stimulus is an applied electrical field, each of the foursubsections may have its own conductive features that may or may not beconnected to the conductive features of the other subsections in themembrane. By assembling the membrane illustrated in FIG. 20 with atleast one and possibly more corresponding membranes and with appropriatespacers, and by connecting the resulting adaptive membrane structure toan appropriate electrical circuit, it is possible to apply an actuatingstimulus to any one, any two, any three or all four of the subsectionsof the membrane structure. In so doing, they will be able to demonstrateat least 5 different states of permeability for such an adaptivemembrane structure with four subsections.

The membrane of FIG. 20 is shown having four similar subsections.However, the individual membranes in a structure need not have exactlythe same subsections. An adaptive membrane structure may be assembledsuch that the individual subsections of one membrane are completelydifferent from other subsections on the same membrane as long as thecorresponding subsections on adjacent membranes have arrays of holesthat are substantially out of registration, or are out of registration,with each other.

A membrane with multiple subsections may be formed by creating an arrayof holes for each subsection on a single continuous sheet of material. Amembrane comprising several subsections may also be formed by firstcreating individual subsection membranes and then joining thesubsections to create a larger sheet or layer. The subsections may bejoined to each other using reactive or non reactive adhesives or usingdifferent welding techniques such as radio frequency welding, ultrasonicwelding and vibration welding.

A further feature of the invention is a means of keeping adjacentmembranes spaced apart during any time when the actuating stimulus isnot applied or operating to move the membranes into contact with eachother. This will produce a gap between the adjacent surfaces of themembranes to enable permeation through the structure as described above.In FIGS. 13A and 13C, a gap 5 between adjacent surfaces 4 and 4′ isshown, and a spacer material 12 is installed between the adjacentmembrane surfaces 4 and 4′, the spacer material being of a shape that itdoes not block the openings to any holes of either membrane surface andhas a thickness that results in the formation of the gap between theadjacent membrane surfaces. Upon application or operation of theactuating stimulus, one or both of the adjacent membranes undergoelastic deformation as depicted in FIGS. 14A, 14B and 14C such that theadjacent surfaces are brought together to provide contact between theadjacent surfaces and seal the holes thereof, in the manner describedabove (compare items 7 and 7′ in FIGS. 13C and 14C). In this context,moreover, the actuating stimulus and the means responsive to theactuating stimulus may be viewed together as means for deforming amembrane to move it into contact with another membrane when a spacer ispresent between the two membranes. Upon release of the actuatingstimulus, however, the elastic energy stored in the deformed membranesis recovered, and the membranes return to their initial position asshown in FIGS. 13A, 13B and 13C whereby the gap 5 between the adjacentmembrane surfaces is restored. This ability to facilitate reformation ofthe gap 5 after removal of the actuating stimulus is a furthercharacteristic of this invention and is termed the “deactuating means”.

Embodiments of the present invention as described above, those forexample shown in FIG. 1, involve at least two largely planar membranesthat, as a result of being moved by the actuating stimulus, contact eachother along adjacent, largely planar, surfaces 4 and 4′ and therebyeliminate a gap 5 that had existed between these surfaces in theunactuated state. The contact of the membranes also eliminates pathssuch as path 6 that, in the unactuated state, would permit enhancedpermeation, convection and/or diffusion associated with the array ofholes incorporated in the base membranes. An alternative embodiment forthe adaptive membrane structure of this invention is shown in FIGS. 15and 16 in the unactuated and actuated states, respectively. In thisembodiment, one or both of two adjacent base membranes contain an arrayof protruding members 21 in the form of a post, knob or bump. In theunactuated state of this embodiment, depicted in FIG. 15, the adjacentbase membranes are separated from each other such that paths forenhanced permeation, convection and/or diffusion such as path 6 exist.However, as shown schematically in FIG. 16, each protruding member 21 inthe array is shaped and positioned so as to be insertable in and enter ahole in the adjacent membrane upon actuation when one or both membranesare moved toward each other. As each protruding member enters itscorresponding hole, it contacts the inner surface of the hole in such away as to create a seal between the protruding member and its matinghole, thereby eliminating paths 6 for permeation, convection and/ordiffusion. As seen in FIG. 16, in this embodiment, the adjacent membranesurfaces 4 and 4′ need not be in contact under application or operationof the actuating stimulus and, furthermore, a gap 5 between thesesurfaces may persist in the actuated state. Although the protrudingmember 21 is shown as a truncated cone in FIGS. 15 and 16, other shapesfor the protruding member may be used, limited only by the need to forma seal against the mating hole surface. Furthermore, although FIGS. 15and 16 depict an array of identical protruding members deployed in aregular square pitch array, no two protruding members in the array needhave identical geometry, and the array pattern for the protrudingmembers is governed by the array pattern of the holes in the adjacentmembrane.

The adaptive membrane structures of this invention can be used ascomponents of articles of apparel, especially for clothing intended toprotect against chemical and biological toxins and pathogens. Sucharticles include without limitation those selected from the groupconsisting of a protective suit, a protective covering, a hat, a hood, amask, a gown, a coat, a jacket, a shirt, trousers, pants, a glove, aboot, a shoe, a shoe or boot cover, and a sock.

The adaptive membrane structure of this invention can also be used inconsumer apparel to protect against the natural elements. In oneembodiment, the structure can be used as an inner liner in responsiveouterwear apparel used for recreational and other outdoor activities,such that the liner could be made to change its permeability dependingupon external temperature and wind conditions, so as to increase thecomfort of the wearer. Examples of such outerwear include withoutlimitation coats, jackets, ski pants, gloves, hats, hoods and masks. Inanother embodiment, a membrane structure of this invention could be usedas a responsive liner in raingear. In dry external conditions, the linerwould be highly permeable, thus breathable, but in wet and rainyconditions, the liner would be made impermeable to externalprecipitation.

The adaptive membrane of this invention could be used for variousmedical applications. In one embodiment, the structure could be used tofabricate items of apparel for health care workers, including withoutlimitation surgical masks, medical or surgical garments, gowns, gloves,slippers, shoe or boot covers, and head coverings.

For some of the aforementioned applications, the adaptive membranestructures of this invention may be used in the absence of anyadditional porous material layers, while for some other applications amulti-layered system may be created where the adaptive membranestructure forms only one component in the multi-layered system. Examplesof porous layers that could be used in conjunction with the adaptivemembrane structure are woven fabrics, non-woven films and porousmembranes. Additional porous layers may be used with the objective of(i) creating a composite system that protects the adaptive membranestructure from an environment that may degrade its performance, and (ii)creating a composite system that has more features than those that canbe offered by the adaptive membrane structure itself.

For example, for the purpose of creating fire retardant apparel thatalso protects a firefighter from noxious fumes and vapors, the adaptivemembrane structure of this invention can be layered with or sandwichedbetween fire retardant fabrics. In this case, the outer fire retardantfabric protects the wearer and the adaptive membrane structure from thefire. For the purpose of creating commercial apparel that protectsagainst the natural elements, the structure of this invention may besandwiched between woven fabrics. The outer and the inner fabric may bechosen to impart a comfortable feel as well as to provide a fashionableappearance to the apparel. Colored and patterned fabrics may also beused as outer layers to introduce additional camouflage feature tochemical and biological protective apparel for the soldier. In somecases, microporous membranes may be used to protect the adaptivemembrane structure from dust and liquids.

An adaptive membrane structure of this invention may be incorporatedinto an article of apparel by any of the knitting, sewing, stitching,stapling or adhering operations known in the art. It is common in theart to use fabrics or other materials having multiple layers from whichto make apparel, and the structure of this invention can be incorporatedtherein by conventional methods.

The potential uses of the adaptive membrane structure of this inventionare numerous and are not limited to protective apparel for humans. Inother embodiments, the adaptive membrane structure of this invention canbe used to create or construct an enclosure for the occupancy of humans,animals or perishables. Such enclosure would include for examplecollective shelters, such as tents, that protect groups of individualsagainst chemical and biological warfare agents. In another embodiment,the invention could be used to set up safe rooms in commercial andresidential buildings. For example, the safe rooms assembled using theadaptive membrane of this invention would be permeable undernon-threatening conditions but would become impermeable when toxicagents are released in the external environment.

The adaptive membranes of this invention may also be used to create anexternal water barrier layer in the construction of commercial andresidential buildings such as dwellings and office buildings. The vaporbarrier, or vapor-retardant layer, in a building should be impermeableenough to prevent precipitation from outside of the building to permeateinside, but yet should be breathable enough to allow excess moisture inthe walls to permeate to the outside. Therefore, in one embodiment, theadaptive membrane of this invention may be used as a responsive vaporbarrier in commercial and residential buildings such that the barrierlayer can exist in multiple states. When there exists excess moisture inthe building walls, the barrier layer would be made vapor permeable, andwhen there is high humidity in the external environment, the barrierlayer would be made impermeable.

Adaptive membranes of this invention, when constructed from transparentpolymer films, could also be used to construct agricultural andhorticultural greenhouses. Temperature control in a greenhouse is animportant issue for optimum plant growth. Existing greenhouses areconstructed from polymer films of low gas and vapor permeability. Sincesuch polymer films are not breathable, the temperature in a greenhouseis conventionally controlled by the opening and closing of engineeredvents. This often leads to undesirable temperature gradients in thegreenhouse. If an adaptive membrane structure is used to construct thegreenhouse, the internal temperature could be more evenly controlled bychanging the permeability of the membrane that envelops the greenhouse.As the temperature in the greenhouse rises, the membrane could be mademore permeable, thereby allowing the process of free convection toreduce the temperature in the greenhouse. Similarly, as the temperaturein the greenhouse falls, the membrane could be made less permeable,allowing the temperature in the greenhouse to rise.

In yet another embodiment, an adaptive membrane structure could be usedin temporary, soft-walled construction, or in permanent construction, tocreate a clean room in which to perform surgical procedures, or in whichto conduct activities requiring high air purity such as computer chipfabrication.

The adaptive membrane of this invention can also be used for managingthe environment in small and large storage areas and containers such asthose used for storing perishables, which include not just ediblematerials but any material that is sensitive to, or may be damaged ordegraded by exposure to, the environment. For example, edible materialssuch as fresh fruits and vegetables may need to be stored under optimumhumidity levels to maintain freshness and enhance their shelf life.Adaptive membranes of this invention could be used to create storageareas or storage containers that respond to the local environmentconditions. For example, when the local water vapor concentration in thestored area is above the desired level, the adaptive membranes willdeactuate to release excess water vapor to the surrounding environment,and will actuate once the water vapor drops below the desired level.Such responsive storage devices could be used to ship edible materialsor other perishables from one place to another or to store them incommercial and residential settings such as cold storage areas andrefrigerators.

Adaptive membrane structures of this invention can also be used toenhance the life and performance of a sensor device, and in this sense asensor device may be viewed as a perishable. The active components in asensor device are very sensitive to their environment and can bepoisoned by liquid or vapor or particulate species in the environment.Such devices can also be corrupted when exposed to high concentrationsof the species they are designed to sense. In one embodiment, anadaptive membrane structure, by its ability to have different states ofpermeability in the actuated and the deactuated states, can be used tocontrol the flow of species to an enclosure housing the active componentof a sensor. In another embodiment, an adaptive membrane structure canbe used as a protective layer or a shroud around the active component.For this application, when it is desired that the sensor be in theactive state for sensing, the adaptive membrane structure may be left inthe unactuated state allowing the active component of the sensor to comein contact with species in the environment that need to be sensed. Butwhen the sensor is no longer in the active or sensing state, theadaptive membrane structure can be deactuated to the closed statethereby protecting the active component of the sensor and enhancing itslife.

An adaptive membrane structure may also be used for controlling the flowof a gas, vapor, liquid and/or particulate such as in valve and airfoilapplications. The structure can be used to modulate the flow of a gasentering a plenum as encountered in heating, air conditioning andventilation systems as well as plenums encountered in industrialprocesses such as the quench system of a fiber spinning process. Inthese applications, the gas flow to be modulated is largely normal tothe membranes of the structure, and the flow rate is altered by changingthe magnitude of the force of that flow, as the actuating stimulus, andthereby altering the resistance to flow of the structure. In addition,the structure can be used to modulate the lift experienced by variousairfoils including those used as sails on sail boats, wind surfers, andother wind powered water craft as well as wings used on powered andun-powered aircraft. In these applications, the gas flow is largelytangential to the membranes of the structure that comprises or isincorporated into the airfoil, and the lift is altered by changing themagnitude of the force of the flow, as the actuating stimulus, therebyaltering the pressure differential across the airfoil.

An adaptive membrane structure can also be used as a valve to controlthe rate of release of a vapor, aerosol or liquid, such as those used asfragrance compounds, perfumes, room fresheners, insecticides, pesticidesor pharmaceuticals. In one embodiment, a controlled release device wouldinclude an adaptive membrane structure, which would separate the agentto be released from the surrounding environment. When the structure isin the deactuated state, the agent would be released to the environmentby means of diffusion and or convection. However, when the structure isin the actuated state, transport of the agent to the environment wouldbe reduced or stopped. The rate of release of the agent would becontrollable by adjusting the frequency with which the structure in thecontrolled release device is oscillated between the actuated state andthe deactuated state.

The use of an adaptive membrane structure of this invention inconnection with physical assets or devices such as enclosures,buildings, sensors and valves can be achieved by fabrication andconstruction methods known in the art. The adaptive membrane structuremay be interleaved between other layers or structural elements such aswhen a building wrap is installed between the interior and exteriorportions of a wall. Or when the adaptive membrane structure is used inan essentially free-standing application such as in a tent, greenhouse,valve or protective cover for a sensor, installation may be achieved byanchoring it to a suitable frame.

The use of the adaptive membrane structure of this invention for valvepurposes enables a method for controlling the flow of gas, vapor, liquidand/or particulates through first and second membranes having holes by(a) providing the holes in each membrane in a position in which, whenthe membranes are in contact with each other, the holes aresubstantially out of registration, or are out of registration, and (b)moving the membranes into contact with each other.

EXAMPLES

The present invention is further defined in the following examples. Itshould be understood that these examples, while indicating preferredembodiments of the invention, are given by way of illustration only.From the above discussion and these examples, one skilled in the artwill be able to ascertain the essential characteristics of thisinvention, and, without departing from the spirit and scope thereof,will be able to make various changes and modifications of the inventionto adapt it to various uses and conditions.

Example 1

This example describes an apparatus and method for testing anddemonstrating the performance of the adaptive membrane structures of theinvention. The multiple states of permeability of the structures aredemonstrated by measuring the ratio of the oxygen permeability in theunactuated state and the actuated state.

Oxygen (O₂) permeability of an adaptive membrane structure is tested ina gas permeability cell, a schematic of which is shown in FIGS. 17A and17B. This system may be used to test any of the embodiments of theinvention described above. For this example, an adaptive membranestructure of the general type shown in FIG. 13 is depicted comprisingtwo substrate membranes 2 and 2′ each modified with an array of holesper the invention and with conductive coatings 7 and 7′ and spacermaterial 12. The membrane assembly is clamped between two cylindrical,clear acrylic pieces 13 and 13′ as shown in FIGS. 17A and 17B. Thelength of each cylindrical piece is 1″ and its inner diameter and outerdiameter are 2.25″ and 3″, respectively. The two cylindrical pieces areheld together by a metallic frame comprising four metal tie rods 14 andtwo metal plates 15 and 15′ that provided complete closure to thepermeability cell except for gas ports as described below. Thecylindrical pieces 13 and 13′ together with the plates 15 and 15′ andthe adaptive membrane structure combined to define two gas volumes 16and 16′ as seen in FIG. 17B. An electrochemical oxygen (O₂) sensor 17with associated electronics 18 (Model GC-501, VICI Metronics, Poulsbo,Wash.) capable of measuring O₂ concentrations in the range of 0.1-25 mol%, is mounted on one of the metal plates 15 such that the active surfaceof the sensor is exposed to the gas volume 16, thereby monitoring the O₂concentration in this volume of the permeability cell; this volume isreferred to herein as “the low concentration side of the permeabilitycell.” The other gas volume of the cell, 16′ (which does not have an O₂sensor) is referred to herein as “the high concentration side of thepermeability cell.”

After the membrane assembly has been mounted in the permeability cell,the two conductive coatings 7 and 7′ are connected, via conductiveelectrical wires 8 fitted with alligator clips, to the output of a highvoltage DC power supply 10 (Model SL10, Spellman High VoltageElectronics Corporation, Hauppauge, N.Y.) capable of delivering tunablebut constant DC voltage between 100 volts and 10,000 volts. During theinitial part of the experiment, when O₂ permeability of the membranestructure in the unactuated state is being measured, the power supply isnot energized.

At the start of the experiment, designated as time zero, a flow of air(consisting of 20.9 mol % O₂) is initiated to the high concentrationside of the permeability cell 16′ through inlet port 19′ and a flow ofnitrogen (N₂ at 99.9% purity) is initiated to the low concentration side16 of the permeability cell through inlet port 19. Each half of the cellalso includes an exhaust port (20 and 20′ in FIG. 17B), each providingfree discharge from its respective gas volume to ambient conditions. Theflow rate of both gases is controlled by separate inline rotometersupstream of the inlet ports 19 and 19′. Care is taken to keep the flowrates of both gases to the two half cells the same and constant duringan experiment. The O₂ concentration in the low concentration side of thecell 16 is then monitored as a function of time. Note that before thestart of the experiment, both halves 16 and 16′ of the permeability cellalways contain ambient air.

At the start of the experiment, when N₂ flow is initiated to the lowconcentration side of the cell 16, the air, and hence the residual O₂present in the half cell, is displaced by N₂. Hence, the O₂concentration in the gas volume 16 drops with time, and after 15 minutesreaches an essentially constant level dependent upon the permeability ofthe unactuated membrane structure. This constant O₂ level indicates thata steady state between the rate of influx of O₂, caused by thepermeation of air through the membrane assembly to the low concentrationside of the cell 16, and the rate of efflux of O₂ through port 20,caused by forced convection out of the low concentration side of thecell, have been achieved.

After 15 minutes have elapsed from the start of the experiment, a knownpotential difference is applied across the conductive coatings 7 and 7′from power supply 10. For the initial few seconds after the voltage isapplied to the circuit, a very small current in the range of a fewmicroamperes is always detected by the ammeter installed in the highvoltage source. After the first few seconds, current is no longerdetected in the circuit thus indicating that the conductive coatings 7and 7′ have become saturated with electrostatic charge. The voltagesource, and consequently the membrane structure connected to the source,is left in the actuated state for 15 minutes. During this time, thechange in the O₂ concentration in the low concentration side 16 of thepermeability cell is monitored. Once the membrane structure is actuatedwith the applied voltage, the oxygen concentration in the lowconcentration side of the cell 16 further drops and reaches a constantvalue depending upon the permeability of the membrane structure in theactuated state.

After the membrane structure has been in the actuated state for 15minutes, the voltage source is turned off, and any residual charge inthe circuit is drained to ground via the voltage source. After thevoltage is turned off, the membrane structure is allowed to stay in theunactuated state for another 15 minutes, during which time the change inoxygen concentration in the low concentration side 16 of thepermeability cell is monitored.

The performance of the adaptive membrane structure is quantified bycalculating the ratio of the O₂ permeability of the membrane assembly inthe unactuated state to the permeability of the same membrane assemblyin the actuated state. This ratio, referred to herein as the figure ofmerit of the membrane assembly, is calculated from the followingequation

$\frac{K_{unactuated}}{K_{actuated}} = \frac{\left( \frac{x_{1}}{x_{o} - {2x_{1}}} \right)_{unactuated}}{\left( \frac{x_{1}}{x_{o} - {2x_{1}}} \right)_{actuated}}$where K is the oxygen permeability of the adaptive membrane structure,the subscript defines the state of the membrane structure (actuated orunactuated), x₀ is the concentration of O₂ in air, and x₁ is theconcentration of O₂ in the low concentration side 16 of the cell whensteady state has been achieved. This equation is derived by conducting amaterial balance of O₂ on both halves of the permeability cell and byassuming that the concentration of O₂ in the respective efflux gasstreams at ports 20 and 20′ is the same as that existing within thecorresponding gas volumes 16 and 16′ of the cell. This equationtypically also provides an indication of permeability that is generallyuseful in all systems.

Example 2

Polyethylene terephthalate film, referred to herein as polyester film,sold under the trade name of Melinex® by DuPont Teijin Films, having athickness of 196 gauge (0.00196″), is coated on one side with a thinlayer of aluminum using a chemical vapor deposition process. Theelectrical resistance of a 2.5″ long by 2″ wide piece of aluminum-coatedpolyester film is measured using a two point probe apparatus. Theresistance of the film is approximately 4 Ohms. The surface of the filmthat includes the aluminum coating will be referred to as the conductivesurface while the other surface that does not have the aluminum coatingwill be referred to as the non-conductive surface. Two circular (4″ indiameter) pieces of this polyester film are converted to a pair ofmembranes following the invention by punching holes through the polymerfilm and the conductive coating thereof. The diameter of the holes is0.04″. Holes are punched using a VIPROS 345 turret punching machinemanufactured by U.S. Amada Ltd. (Buena Park, Calif.). The direction ofthe punching is from the non-conductive surface of the polyester filmtowards the conductive surface. Hence any raised surface features causedby the punching process are predominantly on the conductive surface ofthe polyester film.

In the first membrane, a total of 84 holes are punched while in thesecond membrane 83 holes are punched. The hole pattern in both membranesis a regular square pitch pattern, with center-to-center distancebetween any two nearest neighboring holes being 0.111 inch. The holepattern in each membrane covered 1″×1″ square area in the central regionof the circular film. A major difference between the two membranes isthat the hole pattern in one membrane is offset from the hole pattern inthe other membrane by a distance that is half of the center-to-centerdistance between neighboring holes. This offset is created in both the xaxis and the y axis, where x and y axis are orthogonal to each other andexist in the plane of the membrane. Thus, when the two membranes areprecisely laid on top of each other, all the holes in one membrane areout of registration with all the holes in the other membrane.

An adaptive membrane structure is created by sandwiching a spaceraccording to the invention (see FIG. 13) between the two membranesdescribed above. In particular, the spacer is formed from a stack of twoannular rings each ring having a thickness of 0.004″ and an innerdiameter and an outer diameter of 2.25″ and 4″, respectively. Onefunction of the spacer is to create a finite gap between the membranesand to prevent them from touching each other in the absence of theapplication or operation an actuating stimulus. Another function of thespacer rings is to provide a deactuating force to the membrane structurewhen the voltage is turned off. The spacer rings are created fromtransparent polyethylene terephthalate films sold under the trade nameof Mylar® by DuPont Teijin Films. The two membranes with conductivecoatings and punched hole arrays are stacked such that theirnon-conductive surfaces face each other, and consequently the conductivesurfaces face away from each other. This adaptive membrane structure istested for oxygen permeability, in the unactuated and actuated states,using the method described in Example 1.

First, the oxygen permeability of the membrane assembly in absence ofapplied voltage is tested. After 15 minutes, a potential difference of1000 V is applied across the two conductive coatings on the membranes.When the voltage is applied, the membranes are observed to move,indicating the effect of an actuating stimulus in the form of theinduced voltage. The membrane structure is left in the actuated statefor 15 minutes, and the changes in the O₂ concentration in the lowconcentration side of the cell is monitored.

The voltage is then turned off, and any residual charge is drained fromthe membrane assembly. A few seconds after the voltage source is turnedoff, the membranes are observed to move apart, indicating thedisappearance of any actuating stimulus that has previously moved themembranes towards each other. The membrane structure is left in theunactuated state for 15 minutes and the resulting change in the O₂concentration is monitored.

At the end of this time period, an actuating stimulus is again appliedto the membrane structure in the form of a 1000 V charge. Thisrepetitive cycle of turning on and then turning off the DC voltagesource, and consequently charging the membrane structure with 1000 V andthen discharging it every 15 minutes, is performed two more times. Eachtime the voltage is turned on or off, motion of the membranes isobserved. The cyclical change in O₂ concentration in the lowconcentration side of the cell, caused by cyclical changes in thevoltage-induced permeability of the membrane assembly, is monitored overthe entire duration of this experiment.

The change in O₂ concentration in the low concentration side of thecell, as the input voltage changes, is shown in FIG. 18. Also plotted inthe figure is the cyclical change in the input voltage to the membranecircuit. The y-axis on the left hand side of the figure represents thechanges in O₂ concentration in a logarithmic scale while the y-axis onthe right had side of the figure represents the input voltage on alinear scale. The x-axis represents the elapsed time in minutes.

This example demonstrates that gas permeability of the adaptive membranestructure can be repeatedly changed by application of the appliedvoltage. When a potential difference is applied across the membranestructure and the membranes are electrostatically charged, theconductive coated membranes of this invention are moved toward eachother and “close down” as indicated by the significant reduction in O₂concentration in the low concentration side of the cell. Conversely,when the voltage is turned off and the electrostatic charge is drainedfrom the membrane structure, the membranes “open up” as indicated by thesignificant increase in the O₂ concentration in the low concentrationside of the permeability cell. The steady state O₂ concentration in thelow concentration side of the cell, when the membrane structure of thisexample is in the unactuated state, is 7.7 mol %. Conversely, the steadystate O₂ concentration on the low side of the cell, when the membranestructure is actuated by 1000 V, is only 0.5 mol %. Thus, the figure ofmerit of the adaptive membrane structure of this example, as calculatedfrom the equation described in Example 1, is 56. It should be noted thatif there is no change in O₂ permeability, when the membrane structure isactuated by voltage, the figure of merit would only be 1.

Example 3

A pair of membranes is prepared from the same polyester film withconductive coating that is used for membranes in Example 2. The size ofthe holes, the hole pattern and the hole spacing in the membrane pair ofthis example are the same as those in the membrane pair of Example 2.The only difference between the membrane pairs of this example and themembrane pair of Example 2 is that the holes in the membrane pair ofthis example are created by laser drilling using a Lambda Physik(Göttingen, Germany) excimer laser Model LPX 220I operating at awavelength of 193 nm.

An adaptive membrane structure is created by sandwiching one polyesterspacer ring, 0.004″ in thickness as described in the previous example,between the two membranes. Note that the hole pattern in the twomembranes is offset from each other, and when the membranes areassembled, the holes in one membrane are thus out of registration withthe holes of the other membrane. Also, when the membranes are stacked inthe assembly, the non-conductive surfaces are made to face each other.The membrane structure is mounted and tested in the oxygen permeabilitycell described in Example 1. After the membrane assembly has been testedfor oxygen permeability in the unactuated state, a potential differenceof 1000 V is applied to actuate the membrane assembly. After 15 minutes,the membrane structure is deactuated by turning off the voltage sourceand draining the electrostatic charge from the conductive membranes. Thesteady state O₂ concentration falls from 7.3 mol % in the unactuatedstate to 0.4 mol % when the membrane assembly is actuated by 1000 V. TheO₂ concentration returns back to 7.3 mol % when the voltage is turnedoff. The figure of merit for this membrane assembly is calculated to be58.

Example 4

Two rectangular pieces (6″×5″) of the same polyester film withconductive coating used in Example 2 are washed for one hour in a 5 wt %aqueous solution of DuPont Oxone® monopersulfate compound, obtained fromAldrich Chemical Company, Inc. (Milwaukee, Wis.). This washing processcompletely removes the conductive coating from the surface of the films.The excimer laser apparatus, described in Example 3, is then used todrill holes into the uncoated polyester films. The diameter of theholes, the pattern of holes and the spacing between the holes is thesame as created in the membrane pairs of Example 2 and Example 3.

The membrane pair with conductive coatings from Example 3, the uncoatedmembrane pair from this example and three polyester spacer rings (onebetween each adjacent membrane) are combined to form a membrane assemblycomprising the four membranes. FIG. 19 shows the make up of the membraneassembly. When the assembly is created, care is taken to ensure that (i)all the holes in any given membrane are out of registration with all theholes of its nearest neighbor, and (ii) the membranes with conductivecoatings formed the outer most layers in the assembly.

The oxygen permeability of this assembly in the unactuated state and theactuated state is tested using the permeability cell of Example 1. Apotential difference of 1000 V, applied to the two conductive coatingsof the outer membranes, is used to actuate the membrane assembly. Thesteady state O₂ concentration in the low concentration side of the cell,when the membrane is in the unactuated state, is 4.9 mol %, but when themembrane is in the actuated state, the steady state O₂ concentration isonly 0.2 mol %. This shows that the membranes of this invention can bemade to “close down” when an external voltage is applied. The figure ofmerit of the four-layer membrane of this example is calculated to be 50.This example also demonstrates that the adaptive membrane structures ofthis invention may contain more than two membranes, and that, when anelectrostatic force is the actuating stimulus, membranes serving auseful purpose despite the fact that they do not have a conductivecoating may be present.

Example 5

Two rectangular pieces (6″×5″) of the polyester film with conductivecoating described in Example 2 are punched on the VIPROS punchingmachine to form a pair of membranes, each with an array of 0.04″diameter holes. The holes are punched from the non-conductive side ofthe polyester films. One membrane has a total of 24 holes while thesecond membrane has 21 holes. The hole pattern in both membranes is aregular square pitch pattern, with center to center distance between anytwo nearest neighboring holes being 0.222″. The hole pattern in eachmembrane covered 1″×1″ square area in the central region of the circularfilm. As in Example 2, the hole pattern in one membrane is offset fromthe hole pattern in other membrane by a distance that is half of thecenter to center distance between neighboring holes. This offset iscreated in both the x axis and the y axis direction where the x and yaxis are orthogonal to each other and are contained in the plane of themembrane. Thus, when the two membranes are precisely laid on top of eachother, all the holes in one membrane are out of registration with allthe holes in the other membrane.

An adaptive membrane structure is created by sandwiching four 0.004″thick polyester spacer rings between these membranes. The non-conductivesurfaces of the membranes are assembled to directly face each other. Theperformance of the membrane assembly in the actuated state and theunactuated state is tested in the O₂ permeability cell of Example 1. Themembrane assembly is actuated by 1000 V. When the membrane assembly isin the unactuated state, the steady state O₂ concentration in lowconcentration side of the cell is 5.5 mol %. In the actuated state, thesteady state O₂ concentration is detected to be 0 mol %, which is below0.1 wt %, the lowest O₂ level detectable by the sensor. Hence, thefigure of merit of this membrane assembly is essentially infinity,thereby indicating complete closure.

Example 6

Two rectangular pieces (6″×5″) of 1 mil thick polyimide film, sold byDuPont (Wilmington Del.) under the trade name of Kapton®, are coatedwith Sylgard®184, a two part silicone elastomer formulation sold by DowCorning (Midland, Mich.). The elastomer formulation is prepared bymixing 97 parts of the polydimethylsiloxane (PDMS) polymer with 3 partscrosslinker. The resulting viscous liquid is coated onto the polyimidefilms using a #2.5 Drawdown Rod sold by Paul N. Gardner Company, Inc.(Pompano Beach, Fla.). The wet elastomer coatings are cured for 1 hourin a flow-through convection oven at 100° C. The cured elastomer layermade the polyimide films tacky on one side and hence allowed them toadhere to other smooth surfaces. A circular hole, 2″ in diameter, ispunched in the central region of each of the polyimide films. Thesefilms are then set aside to serve as stencils for coating polyesterfilms as described below.

Two rectangular pieces (6′×5″) of polyester film with conductive coatingas described in Example 2, are washed in methanol to remove any residualoil or grease from the film surfaces. The dry films, with the conductivesurface facing downwards, are laid on to a clean and smooth glasssurface. The two elastomer-coated polyimide stencils, as describedabove, are laid over with the tacky surface facing the polyester filmsand then made to adhere to the non-conductive surfaces of the polyesterfilms. Now only the 2″ circular region in the center of each of thepolyester films is exposed, while the other parts of the polyester filmsare covered with the polyimide films. The resulting bilayer films arecoated with Elastosil® 6238 silicone elastomer formulation sold byWacker Silicones (Munich, Germany). The formulation is prepared bymixing 97 parts of PDMS with 3 parts of the crosslinker. A #2.5 DrawdownRod is used for creating a uniform coating. Immediately after thecoating step, the polyimide stencils are carefully peeled away from thepolyester films, thus leaving behind a 2″ circular patch of a wetsilicone elastomer coated on the nonconductive surface of each polyesterfilm. The elastomer coating is cured at 100° C. for 1 hr. The averagethickness of the cured elastomer layer is 0.0025″.

Arrays of holes are added to the pair of elastomer coated polyesterfilms by punching using the same machine used in Example 1. The holediameter, hole spacing and hole pattern are the same as in the membranepair of Example 2. Holes are punched from the elastomer-coated surfacetowards the conductive surface.

An adaptive membrane structure is created by sandwiching two 0.004″thick polyester spacer rings between the elastomer-coated membranes. Themembranes are assembled such that the elastomer-coated surfaces arefacing each other. The performance of the membrane is tested in the O₂permeability cell of Example 1. The steady state O₂ concentration in thelow concentration side of the cell, when the membrane assembly is in theunactuated state, is 7.7 mol %. When the membrane assembly is actuatedby 2000 V, the steady state O₂ concentration drops to 0.1 mol %. Thefigure of merit of this membrane assembly is, therefore, calculated tobe 290.

Example 7

A roll of polyvinylidene fluoride (PVDF) film, 0.003 inches inthickness, is obtained from Westlake Plastics Company (Lenni, Pa.). Onesurface of this PVDF film is very smooth while the other surface isrough. Two rectangular pieces (6″×5″) are cut from the PVDF film rolland washed in methanol. The films are then heat treated by placing themin a heated convection oven at 120° C. for 1 hour. The rough sides ofthe films are then made electrically conductive by depositing analuminum layer using a chemical vapor deposition process. The thicknessof the aluminum layer could not be measured accurately because of theinherent roughness of the PVDF film surface. However, sufficientaluminum is deposited such that the resulting film became opticallyopaque, and they offered electrical resistance of a few ohms whenelectrodes of a multimeter are placed 4″ apart at the edges of themetallic surface of the aluminum coated PVDF film.

Arrays of holes are added to the pair of PVDF films with conductivecoatings by laser drilling using the excimer laser described in Example3. Holes are drilled from the smooth surface of the PVDF films. The sizeof the holes, the spacing of the holes and the hole pattern in themembranes is the same as used for the membrane pair in Example 2. Afterthe drilling step, each PVDF membrane is sandwiched between theoptically flat and mirror smooth surfaces of two silicon wafers. Thesandwich thus created is placed between the heated plates of a hydraulicpress. The temperature of the plates is held at 120° C. When the siliconwafers have reached a steady state temperature, the wafer sandwich iscompressed for 2 minutes at an applied stress of 314 lb/in². Thiscompression process helps to reduce surface deformities in the membranesthat may have been created by the laser drilling process.

An adaptive membrane structure is created by sandwiching two 0.004″thick polyester ring spacers between the PVDF membranes. In the membraneassembly, the non-conductive surfaces of the PVDF membranes directlyface each other. The membrane assembly is tested in the O₂ permeabilitycell of Example 1. The steady state O₂ concentration in the lowconcentration side of the cell, when the membrane assembly is in theunactuated state, is 7.8 mol %. When the Membrane assembly is actuatedby 1000 V, the steady state O₂ concentration dropped to 0.2 mol %. Thefigure of merit of this membrane assembly is calculated to be 151.

Example 8

This example describes a lithographic method for printing discreteelectrically conductive features onto a flexible polymer film. Theelectrical circuit or artwork that is to be printed onto a flexiblepolymer film is first transferred to a negative photomask. A 0.002″thickpolyimide film having a thin conductive copper coating on one side ofthe film, sold under the trade name of Pyralux® TM by DuPont (WilmingtonDel.), is used as the substrate onto which the conductive circuit is tobe printed.

This flexible conductive film is sequentially washed in (i) Versa-Clean®415 solution (Fisher Scientific International Inc., Hampton, N.H.) at45° C., (ii) deionized water at room temperature, (iii) Sure Etch 550acidic copper etchant (Dayton Superior, Kansas City, Kans.) at 35° C.,and (iv) deionized water at room temperature. The clean copper surfaceof the flexible conductive film is then laminated to a Riston® 9415photoresist film using a Vacrel® SMVL-100 vacuum laminator (both fromDuPont). The negative photomask is laid on top of the photoresist film,and the photoresist is then exposed to ultraviolet light in a Riston® PCprinter 130. The total energy density for the exposure is 100mJoule/cm².

The exposed film/photoresist laminate is now developed in a ChemcutSystem CS-2000 developer (Chemcut Corporation, State College, Pa.) at aspeed of 77 inch/minute. The developing solution consists of 1 wt % ofsodium carbonate in deionized water. The temperature of the developingsolution is 85° F. (29° C.). The developed film is then washed in a 5 wt% solution of DuPont Oxone® monopersulfate compound (Aldrich) in wateruntil all the exposed copper from the polyimide surface had beenstripped. In the final step, the photoresist layer is stripped bywashing the polyimide film in 3 wt % solution of potassium hydroxide inwater. All the features that are originally present in the negativephotomask are now imprinted as conductive features on the polyimidefilm.

Example 9

This example demonstrates an adaptive membrane structure in whichelectrodes are formed from a network of discrete but interconnectedelectrically conductive lines that have been printed on the film surfaceusing the lithographic process described in Example 8.

Two separate but matching circuit patterns, one for each membrane in theadaptive membrane structure, are drawn to the same length scale asdesired in the final electrical circuit on the membranes. The circuitpattern for each membrane consists of 200 equal size circular ringsprinted in a regular face centered square pitch pattern andinterconnected by straight lines to complete the electrical circuit asschematically depicted in FIG. 8. The inner diameter and outer diameterof the circular rings in the pattern are 0.051″ and 0.070″,respectively. The center-to-center distance between the nearestneighbors and the next nearest neighbors are 0.079″ and 0.111″,respectively. The circular rings are connected by 0.1 mm thick lines.The two circuit patterns are printed onto circular discs of Pyralux® TMfilm. The circuit pattern on one film is a mirror image of the circuitpattern on the second film. Hence, when the two patterns are preciselylaid on top of each other such that the two film surfaces that supportedthe conductive features are directly facing each other, all 200 rings inone film precisely overlapped with all 200 rings in the other film.

The excimer laser described in Example 3 is now used to create an arrayof holes in the films with the matching circuit pattern. A total of 100equal sized holes, 0.04″ in diameter, in a 10 hole×10 hole regularsquare pitch pattern, are drilled in each film. All holes are drilledsuch the circular conductive features completely encircled each hole(see FIG. 8). The center to center spacing between any two neighboringholes is 0.111″. The hole pattern in one membrane is offset from thehole pattern in the other membrane by a distance that is half of thecenter to center distance between neighboring holes. This offset iscreated in both the x axis and the y axis directions where the x and yaxis are orthogonal to each other and are contained in the plane of themembrane. Thus, when the two membranes are precisely laid on top of eachother, all the holes in one membrane are out of registration with allthe holes in the other membrane.

An adaptive membrane structure is created by sandwiching two 0.004″thick polyester spacer rings between the pair of membranes. In themembrane assembly, the non-conductive surfaces of the membranes are madeto face each other. The membrane assembly is tested in the O₂permeability cell described in Example 1. In the unactuated state, thesteady state concentration of O₂ in the low concentration side of thecell is 8.9 mol %. When the membrane is actuated by 2000 V, the steadystate O₂ concentration dropped to 0.5 mol %. The figure of merit for themembrane assembly of this example is calculated to be 114.

Where an apparatus or method of this invention is stated or described ascomprising, including, containing, having, being composed of or beingconstituted by certain components or steps, it is to be understood,unless the statement or description explicitly provides to the contrary,that one or more components or steps other than those explicitly statedor described may be present in the apparatus or method. In analternative embodiment, however, the apparatus or method of thisinvention may be stated or described as consisting essentially ofcertain components or steps, in which embodiment components or stepsthat would materially alter the principle of operation or thedistinguishing characteristics of the apparatus or method would not bepresent therein. In a further alternative embodiment, the apparatus ormethod of this invention may be stated or described as consisting ofcertain components or steps, in which embodiment components or stepsother than those as stated or described would not be present therein.

Where the indefinite article “a” or “an” is used with respect to astatement or description of the presence of a component in an apparatus,or a step in a method, of this invention, it is to be understood, unlessthe statement or description explicitly provides to the contrary, thatthe use of such indefinite article does not limit the presence of thecomponent in the apparatus, or of the step in the method, to one innumber.

1. A multi-layer garment for protection of a wearer, selected from thegroup consisting of a protective suit, a protective covering, a hat, ahood, a mask, a gown, a coat, a jacket, a shirt, trousers, pants, aglove, a boot, a shoe and a sock, said garment comprising: at least onelayer that consists essentially of an adaptive membrane structure,incorporated into the garment, comprising a first membrane having holes,a second membrane having protruding members and an array of holes, andmeans responsive to an actuating stimulus that moves one membrane towardthe other membrane, wherein the protruding members are positioned on thesecond membrane to be insertable in the holes on the first membrane whenone membrane is moved toward the other, such that paths for enhancedpermeation, convection and/or diffusion through both membranes existwhen the adaptive membrane structure is in an unactuated state and theholes are sealed by the protruding members when the adaptive membranestructure is in an actuated state in response to the actuating stimulus,thereby protecting the wearer from hazardous agents in the environment.2. The multi-layer protective garment of claim 1 wherein the actuatingstimulus is an electrostatic force, magnetic force, hydrostatic force orhydrodynamic force.
 3. The multi-layer protective garment of claim 1wherein one or both membranes have an electrically conductive coating ona surface thereof.
 4. The multi-layer protective garment of claim 3wherein the conductive coating is applied in a pattern that coversselected areas of a membrane's surface.
 5. The multi-layer protectivegarment of claim 3 wherein the conductive coating is itself coated withone or more layers of dielectric material.
 6. The multi-layer protectivegarment of claim 1 wherein the structure further comprises one or morespacers between the membranes wherein no spacer blocks a hole.
 7. Themulti-layer protective garment of claim 1 further comprising a sensorthat detects a change in the environment in which the structure islocated.
 8. The multi-layer protective garment of claim 7 wherein thesensor detects a change in temperature, a change in humidity, or achange in the concentration of a selected chemical, biological orparticulate species.
 9. The multi-layer protective garment of claim 1further comprising a sensor that activates the actuating stimulus. 10.The multi-layer protective garment of claim 1 wherein the actuatingstimulus operates to a substantially uniform extent on all portions ofthe first membrane.
 11. The multi-layer protective garment of claim 1,which is impermeable to a selected human pathogen or toxin in itsactuated state.
 12. The multi-layer protective garment of claim 1, whichis permeable to water, vapor in its actuated state.
 13. The multi-layerprotective garment of claim 1 further comprising one or more membranesin addition to the first and second membranes, and/or one or more layersof fabric.
 14. The multi-layer protective garment of claim 1 wherein atleast one membrane comprises at least one polymer.
 15. The multi-layerprotective garment of claim 1 wherein at least one membrane comprises atleast one member of the group consisting of activated carbon, highsurface silica, molecular sieves, xerogels, ion exchange materials,powdered metal oxides, powdered metal hydroxides, and antimicrobialagents.
 16. The multi-layer protective garment of claim 1 wherein boththe first and second membranes contain an array of protruding members.17. The multi-layer protective garment of claim 1, further comprisingleast one additional layer comprising a fabric, a film, or a membrane.